In computing, a queue refers to a sequence of work objects that are waiting to be processed. Email also features a queue which follows this principle. For email, a queue is where email messages wait to be processed by the recipient’s mail server after they are scheduled for delivery. These message queues provide what is commonly known as an asynchronous communications protocol; this means that message’s sender and receiver do not need to interact with the queue at the same time. Instead, the message can stay in the queue until the point when the recipient is ready to retrieve it. Because the queue, by necessity, works as temporary storage, there may be limits on the size of data that may be transmitted in a single message or on the number of messages that may remain in the queue at one time.

To interact with the queue, a system administrator will install a queue manager to define the message queue. An application will then ‘listen’ for messages to be placed into the queue. A second application will then connect to the queue and transfer the message into it. The queue manager stores the messages until the receiving application (from the recipient’s end) connects to the queue to receive the messages.